To support FCC E911 rules to locate wireless 911 callers, as well as to support other location-enabled services, some providers of wireless communication services are installing mobile appliance location capabilities into their wireless networks. These wireless networks typically include at least one base station. One such type of mobile appliance location system is known in the art as a network overlay location system. Such systems typically, but not necessarily, include the addition of some software and/or hardware systems to the base stations of the wireless networks. In operation, these network overlay location systems may include one or more wireless location sensors (“WLS”) which may take certain measurements of RF transmissions from a mobile appliance for which the geolocation is desired. The network overlay system may also include a geolocation control system (sometimes referred to as a geolocation control server) (“GCS”) which may estimate the location of the mobile appliance based at least in part on the measurements obtained by the WLSs. The WLSs and/or the GCS may be co-located with the base station of the wireless network. Furthermore, the location of the mobile appliance may be determined with respect to one or more base stations. Since the geographic location of the base stations is typically known, the determination of the location of the mobile appliance with respect to the base station permits the geographic location of the mobile appliance to be determined. Similarly, if the geographic location of the WLS is known, then the location of the mobile appliance with respect to the WLS may be determined. The RF measurements of the transmitted signal at the WLS may include, but is not limited to, the time-of-arrival, time difference of arrival, angle of arrival, signal power, or unique/repeatable radio propagation path (radio fingerprinting) derivable features. In addition, some geolocation systems can also use collateral information, e.g., information other than that derived from the RF measurement to assist in the geolocation of the mobile appliance, i.e., location of roads, dead-reckoning, topography, map matching, etc.
As used herein, a mobile appliance may be, but is not limited to, any one or more of the following: laptop computer, mobile telephone, mobile radio, walkie-talkie, personal digital assistant, pager, personal tracking device, vehicle, automotive anti-theft device, telemetry device, fleet tracking device, anti-location fraud device, or any other similar device or system for which the geolocation of the device or system is desired.
In a network-based geolocation system, the mobile appliance to be located is typically identified and radio channel assignments determined by, for example, monitoring the control information transmitted on a radio channel for telephone calls being placed by the mobile appliance to detect calls of interest, e.g., 911 calls, or a location request provided by a non-mobile appliance source, i.e., an enhanced services provider. Once a mobile appliance to be located has been identified and radio channel assignments determined, the location determining system is tasked to determine the geolocation of the mobile appliance, and report the determined position to an appropriate entity, such as a mobile call center or enhanced services provider.
Some prior art systems are mobile appliance-based and determine the position of the mobile appliance by receiving multiple dedicated location signals either from components outside the mobile appliance's communication system, such as satellites and GPS systems or from a network of dedicated land-based antennas. Other prior art geolocation systems that are network overlay, or infrastructure-based, systems use combinations of specific, as opposed to ambiguous, measurements generally from multiple base stations, such as angle of arrival, time-of-arrival, and time-difference-of-arrival. These specific measurement values are used to solve a set of mathematical equations to determine the location of the mobile appliance.
One prior art example of geolocation is based on time-difference-of-arrival (“TDOA”) of radio signals at a plurality of base stations. One prior art TDOA system is described in U.S. Pat. No. 5,327,144 to Stilp, et al. Another type of TDOA system is described in U.S. Pat. No. 5,317,323 to Kennedy, et al. for which the present inventor is a co-inventor. TDOA systems, such as the two previously mentioned and others, measure the time-of-arrival at a single or multiple antennas at a plurality of base stations of a radio signal emitted by a transmitter. The time-of-arrival is used to define sets of hyperbolic surfaces which determine possible locations of the transmitter between each pair of base stations receiving the radio signal. The intersection of these hyperbolic surfaces defines the location of the transmitter. The underlying technique of TDOA systems relies on geometric equations and the constant speed of the radio signal.
As mentioned above, the prior art systems rely on determining a channel assignment by monitoring the control information transmitted on a radio channel for telephone calls being placed by the mobile appliance to thereby detect calls of interest or a location request provided by a non-mobile appliance source, e.g., an enhanced services provider. In either case the identification of the mobile user and its channel assignment necessitate retrieval of information bits from the mobile appliance, through control signals or call setup information. However with the advent of the third generation CDMA specification known in the art as CDMA2000, a new system and method can be used to determine the location of a mobile appliance independent of the information data bits transmitted by the mobile appliance.
Idealized wireless systems operating under the IS-95 standard and the IS-2000 standard are shown pictorially in FIGS. 1 and 2, respectfully. The IS-95A/JStd-008 offers one physical structure using the forward channels, Pilot 101, Synchronization 103, Paging 105 and Traffic 107 from a base station 111; and reverse channels, Access 102 and Traffic 104 from the mobile appliance 110.
The IS-2000 standard in FIG. 2 includes numerous common and dedicated channels in both the forward and reverse direction. The forward channels include Pilot 201, Sync 203, Paging 205, Control 207, Auxiliary Pilot 209, Quick Paging 213, and Broadcast 215 as common channels and Auxiliary Pilot 217, Control 219, Fundamental 221, and Supplemental 223 as dedicated channels from the base station 211. The reverse channels include Access 202 and Control 204 as common channels and Pilot 206, Control 208, Fundamental 212 and Supplemental 214 as dedicated channels from the mobile appliance 210.
In a system operating under the IS-95 standard, the forward link uses the pilot, paging, and sync control channels to maintain the link while the forward traffic channel is used for data and voice communication. On the reverse link, the mobile access channel is used to gain access to the system and the traffic channel is used for data and voice transfer.
In a system operating under the CDMA2000 IS-2000 standard, the IS-95 forward link channels are used in addition to a dedicated reverse pilot channel from the mobile appliance to the base station. The reverse pilot signal is unique for each mobile appliance and is typically a function of the Electronic Serial Number (“ESN”). The reverse pilot signal identifies the mobile appliance and typically incorporates a time reference so subsequent data sent by the mobile appliance can be very quickly decoded at the base station. The reverse pilot channel typically is used, for example, for coherent demodulation, multi-source combining, and identification of a mobile appliance. For IS-95 systems, a network overlay geolocation system for geolocating a mobile appliance typically entailed transferring a large amount of information through the geolocation system in order to geolocate a mobile appliance.
The ESN of a mobile appliance may typically be determined, as is known in the art, from the location requesting entity (which is separate from the wireless communication system), from control channels, from certain signaling present in the wired portion of the wireless communication system, or other such methods.
The details of the reverse pilot signal in a CDMA2000 wireless communication system are established by the Telecommunications Industry Association (“TIA”), as is known to those of skill in the art.
The existence of the reverse pilot channel in IS-2000 communication systems presents a new resource for efficiently geolocating a mobile appliance. Therefore, there is a need in view of the functionality afforded by the new CDMA2000 specifications to utilize the characteristics of the reverse pilot channel in creating a system and method for geolocating a mobile appliance operating in a wireless communication system under the CDMA2000 specifications.
In order to obviate the deficiencies in the prior art it is an object of the present disclosure to present an improved method of determining the location of a mobile appliance in a wireless communication system having plural receiver stations (e.g., base stations) for communicating with the mobile appliance, including a reverse pilot signal transmitted by the mobile appliance to be used by the receiving stations to coherently demodulate the mobile appliance's transmissions. The improvement comprising determining the location of the mobile appliance based on the time difference of arrival of the reverse pilot signal at one or more geolocating receivers (e.g., WLS).
It is also an object of the present disclosure to present a novel method of geolocating a mobile appliance in a wireless communication system having plural receiver stations for communicating with at least one mobile appliance wherein the communication system has a reverse pilot channel used by the plural receiver stations for coherently demodulating transmissions from the mobile appliances operating in the system. The method for determining the location of a respective one of the mobile appliances (i.e., the target mobile) includes the step of determining the time difference of arrival of a reverse pilot signal transmitted by the target mobile and received on the reverse pilot channel at one or more WLS.
It is another object of the present disclosure to present a novel method for estimating the location of a mobile appliance in a wireless communication system having plural base stations for communication with the mobile appliance. The method includes providing a reverse pilot channel and transmitting from the mobile appliance a reverse pilot signal over the reverse pilot channel for reception at one or more WLS. A GCS is also provided and used for determining the time of arrival of the reverse pilot signal at the one or more WLS. The GCS also determines a difference in time-of-arrival of the pilot channel at the one or more WLS and estimates the geolocation of the mobile appliance therefrom.
It is still another object of the present disclosure to present a novel mobile appliance location determining system as a network overlay to a wireless communication system including one or more base stations. The communication system includes multiple mobile appliances each transmitting a unique non-traffic signal. The network overlay system includes plural WLSs, one or more of which receive the non-traffic signal from the target mobile (i.e., the mobile appliance for which the geolocation is desired to be determined or estimated), and a geolocation processor (typically a GCS) in communication with the WLSs. The geolocation processor includes a reference signal generator for generating a reference signal, a cross-correlation device for determining time of arrival at one or more of the WLSs of the non-traffic signal from the target mobile, and a location estimator for estimating the location of the mobile appliance based on the time of arrival of the non-traffic signal from the target mobile at the one or more WLSs. The cross-correlation device may determine time of arrival based on a correlation of the non-traffic signal with the reference signal. Additionally, the WLSs need not be collocated with any of the base stations in the communication system.
It is yet another object of the present disclosure to present a novel method for determining the location of a target mobile appliance in a wireless communication system including one or more base stations wherein multiple WLSs are used to determine the location of the target mobile. The method includes transmitting from the target mobile a known spread spectrum sequence for establishing base station synchronization and receiving the sequence at one or more of the WLSs. The method further includes correlating the received spread spectrum sequence with a reference sequence to determine the time of arrival at each of the one or more WLSs, and estimating the location of the mobile appliance based on the time difference of arrival at of the spread spectrum sequence at the one or more WLSs.
It is an additional object of the present disclosure to present a novel mobile appliance location determining system in a wireless communication system including one or more base stations and having one or more mobile appliances emitting a dedicated reverse pilot signal on a reverse pilot channel. The location determining system includes one or more WLS that receive the reverse pilot signal of the target mobile wherein each of the one or more WLS is operatively connected to a geolocation processor in a GCS. The GCS includes a reference signal generator, a cross-correlation device, and a location estimator. The signal generator generates a reference signal based on the unique code mask of the target mobile, which is typically a function of the ESN of the target mobile. The cross-correlation device determines the time of arrival of the reverse pilot signal of the target mobile that is received over the reverse pilot channel at each of the one or more WLSs by correlating the received reverse pilot signal with the reference signal. The location estimator estimates the location of the target mobile based on the time of arrival and/or the time difference of arrival between sets of WLSs.
It is yet an additional object of the present disclosure to locate a mobile appliance whether or not the mobile appliance is engaged is transmitting/receiving voice traffic signals, data traffic signals, or no traffic signals. In other words, the inventive system and method of the present disclosure is capable of locating a mobile appliance independent of the “state” or “mode” of the mobile appliance.
One purpose of this disclosure is the location of a mobile appliance in a wireless communication system for the purpose of satisfying FCC E911 guidelines as well as other location based service guidelines. The embodiments presented may also deal with the location of mobile appliances that either continuously or periodically transmit known spread spectrum sequences, independent of the information data bits (i.e., traffic signal) being transmitted to/between the mobile appliance and/or a base station.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.